@spec activated(t(), Req.Response.t()) :: [module()]

Returns the configured extension modules whose URI appears in the server's A2A-Extensions response header.

@spec cancel_task(target(), String.t(), keyword()) ::
  {:ok, A2A.Task.t()} | {:error, term()}

Cancels a task by ID via CancelTask.

Options

• :headers — additional HTTP headers
• :timeout — HTTP request timeout in ms

Examples

{:ok, task} = A2A.Client.cancel_task(client, "tsk-abc123")

@spec delete_push_config(target(), String.t(), String.t(), keyword()) ::
  :ok | {:error, term()}

Deletes a push notification config. Idempotent — deleting a config that is not registered succeeds.

Options

• :headers — additional HTTP headers
• :timeout — HTTP request timeout in ms

@spec discover(String.t(), keyword()) :: {:ok, A2A.AgentCard.t()} | {:error, term()}

Discovers an agent by fetching its agent card.

Sends GET /.well-known/agent-card.json and decodes the response into an %A2A.AgentCard{}.

Options

• :headers — additional HTTP headers
• :timeout — HTTP request timeout in ms
• :agent_card_path — custom discovery path (default: "/.well-known/agent-card.json")

Examples

{:ok, card} = A2A.Client.discover("https://agent.example.com")
card.name #=> "my-agent"

@spec get_push_config(target(), String.t(), String.t(), keyword()) ::
  {:ok, A2A.PushNotificationConfig.t()} | {:error, term()}

Retrieves a push notification config by task ID and config ID.

Options

• :headers — additional HTTP headers
• :timeout — HTTP request timeout in ms

@spec get_task(target(), String.t(), keyword()) ::
  {:ok, A2A.Task.t()} | {:error, term()}

Retrieves a task by ID via GetTask.

Options

• :history_length — number of history entries to include
• :headers — additional HTTP headers
• :timeout — HTTP request timeout in ms

Examples

{:ok, task} = A2A.Client.get_task(client, "tsk-abc123")

@spec list_push_configs(target(), String.t(), keyword()) ::
  {:ok, [A2A.PushNotificationConfig.t()]} | {:error, term()}

Lists every push notification config registered for a task.

Options

• :headers — additional HTTP headers
• :timeout — HTTP request timeout in ms

@spec new(A2A.AgentCard.t() | String.t(), keyword()) :: t()

Creates a new client struct.

Accepts a URL string or %A2A.AgentCard{}. Options are forwarded to Req.new/1 for customizing the HTTP client (headers, timeouts, etc.).

Examples

client = A2A.Client.new("https://agent.example.com")
client = A2A.Client.new(card, headers: [{"authorization", "Bearer token"}])

@spec parse_extensions_header(Req.Response.t()) :: [String.t()]

Parses the A2A-Extensions header from a Req.Response. Returns the list of extension URIs the server activated for the corresponding request, or [] if the header is absent.

HTTP headers may appear as a single comma-separated value or as multiple repeated headers; both are handled.

@spec resubscribe(target(), String.t(), keyword()) ::
  {:ok, Enumerable.t()} | {:error, term()}

Reattaches to a running task's event stream via SubscribeToTask.

Returns {:ok, stream} for a task still in progress. The first element is the task as it stands; subsequent elements are %A2A.Event.StatusUpdate{} structs, and the stream ends when the task reaches a terminal state.

A task that does not exist answers TaskNotFoundError and one that has already finished answers UnsupportedOperationError — both come back as {:error, %A2A.JSONRPC.Error{}} rather than an empty stream.

Events produced before the subscription are not replayed, so a caller that needs the full history should pair this with get_task/3.

Options

• :history_length — number of history entries to include in the snapshot
• :headers — additional HTTP headers
• :timeout — HTTP request timeout in ms

Examples

{:ok, stream} = A2A.Client.resubscribe(client, "tsk-abc123")
Enum.each(stream, &IO.inspect/1)

@spec send_message(target(), A2A.Message.t() | String.t(), keyword()) ::
  {:ok, A2A.Task.t() | A2A.Message.t()} | {:error, term()}

Sends a message to an agent via SendMessage.

Returns {:ok, task} on success, or {:ok, message} when the agent answers out-of-band with a bare %A2A.Message{} — SendMessageResponse is a Task/Message oneof, so match on the struct to tell them apart. Returns {:error, reason} on failure. The message can be a string, an %A2A.Message{}, or a list of parts.

Options

• :task_id — continue an existing task
• :context_id — set the context ID
• :configuration — MessageSendConfiguration map
• :metadata — arbitrary metadata map
• :headers — additional HTTP headers
• :timeout — HTTP request timeout in ms

Examples

{:ok, task} = A2A.Client.send_message(client, "Hello!")
{:ok, task} = A2A.Client.send_message(client, "More info", task_id: task.id)

@spec set_push_config(target(), A2A.PushNotificationConfig.t(), keyword()) ::
  {:ok, A2A.PushNotificationConfig.t()} | {:error, term()}

Registers a push notification config for a task.

The config's :task_id names the task; :id is assigned by the server when left nil. Returns the stored config.

Options

• :headers — additional HTTP headers
• :timeout — HTTP request timeout in ms

Examples

config = %A2A.PushNotificationConfig{
  task_id: "tsk-abc123",
  url: "https://example.com/webhook",
  authentication: %{scheme: "Bearer", credentials: "s3cret"}
}

{:ok, stored} = A2A.Client.set_push_config(client, config)

@spec stream_message(target(), A2A.Message.t() | String.t(), keyword()) ::
  {:ok, Enumerable.t()} | {:error, term()}

Sends a message and returns a stream of decoded SSE events.

Uses SendStreamingMessage to receive server-sent events. Returns {:ok, stream} where the stream yields decoded structs (%A2A.Task{}, %A2A.Event.StatusUpdate{}, %A2A.Event.ArtifactUpdate{}, or %A2A.Message{}).

Options

Same as send_message/3.

Examples

{:ok, stream} = A2A.Client.stream_message(client, "Count to 5")
Enum.each(stream, fn
  %A2A.Event.StatusUpdate{final: true} -> :done
  event -> IO.inspect(event)
end)

@spec version(Req.Response.t()) :: String.t() | nil

Returns the negotiated A2A protocol version from the server's A2A-Version response header, or nil if the header is absent.